The present invention relates to the technology for biomeasurement using light that uses light to acquire intracorporeal information. More particularly, the present invention is concerned with the technology for biomeasurement using light that makes it possible to dispose a probe at a position at which high sensitivity is exhibited so as to thus improve positional reproducibility to be ensured at the time of remounting the probe.
Optical bioinstrumentations for living body are such that a light incidence/light detection probe is mounted on a region to be measured in order to acquire intracorporeal information. For example, a technology of acquiring spatiotemporal information on brain activities using near-infrared light with a plurality of light incidence/light detection probes mounted on a subject's head (refer to, for example, Non-Patent Document 1: “Medical Physics” written by A. Maki et al. (vol. 22, pp. 1997-2005, 1995). According to the technology, the near-infrared light incident on the scalp is detected at a distance of about 3 cm in order to measure a change in the concentration of hemoglobin in the cerebral cortex interposed between the incident point and the detection point. Since the local hemodynamics, that is, the concentration of hemoglobin varies depending on a brain activity, the spatiotemporal change of brain activities can be grasped. What counts in the measurement of brain activities is to learn in what cerebral region an activity takes place.
However, since the optical bioinstrumentation for living body cannot acquire anatomical information, an active region must be detected based on positional information acquired using other technique. Hereinafter, an image to be used to observe the shape or structure of the brain is called an anatomical image, and an image used to observe the state of brain activities by analyzing cerebral blood flows or any other information is called a brain functional image. As a modality for constructing the anatomical image, magnetic resonance imaging (MRI) or X-ray computed tomography (CT) may be adopted. Moreover, as a modality for constructing the brain functional image, in addition to the optical bioinstrumentation for living body, functional MRI (fMRI), positron emission tomography (PET), electroencephalography (EEG), magnetoencephalography (MEG), or single photon emission computed tomography (SPECT) may be adopted.
In a conventional optical bioinstrumentation for living body, a method for displaying an image, which expresses brain activities and is constructed by the optical bioinstrumentation for living body, while superimposing the image on a three-dimensional anatomical image constructed through MRI or X-ray CT has been proposed (refer to, for example, Patent Document 1: Japanese Patent Application Laid-Open No. 2001-198112). In order to construct the three-dimensional anatomical image, a reference point mark is drawn at a specific point on a subject. A three-dimensional position sensor such as a magnetometric sensor is used to measure coordinate values representing the position of the light incidence/light detection probe. The image expressing brain activities is positionally associated with the three-dimensional anatomical image using the position of the reference point mark as a reference.
As a technology making it possible to improve positional reproducibility to be ensured at the time of remounting a probe, a head gear for biomeasurement using light which includes a means for measuring a relative distance from an external marker of a subject has been proposed (refer to, for example, Patent Document 2: Japanese Patent Application Laid-Open No. 2004-194701). A measure that reads the relative distance between external markers is included in the shell of the head gear, and a light incidence/light detection probe is positioned according to the reading of the measure. In the technology, the probe can be easily positioned without the necessity of an anatomical image constructed by other modality.
The optical bioinstrumentation for living body detects near-infrared light, which is irradiated through an incident point on the scalp, at a detection point located at a distance of approximately 3 cm. Herein, a midpoint between the incident point and detection point is regarded as a sampling point. Moreover, a topographic image constructed based on measurement signals acquired from a plurality of sampling points is used to display the spatial distribution of brain activities. An experiment performed using a phantom has demonstrated that sensitivity expressed in the topographic image varies depending on a difference in the positional relationship between the sampling point and an activated area in the brain (refer to, for example, Non-Patent Document 2: “Physics in Medicine and Biology” written by T. Yamamoto et al. (vol. 47, pp. 3429-3440, 2002).